Fuel composition

ABSTRACT

A fuel composition comprising: a diesel base fuel; from 1 to 10% v/v of a fatty acid alkyl ester; and more than 10% v/v of an ether component, the ether component comprising one or more ether compounds having in the range of from 8 to 12 carbon atoms and selected from compounds of formula I 
       R 1 —O—R 2   (I)
 
     wherein R 1  and R 2  are independently primary or secondary alkyl.

This present application claims the benefit of European Application No.12183067.3, filed Sep. 5, 2012.

FIELD OF THE INVENTION

This invention relates to diesel fuel compositions comprising certainethers, their preparation and their use, as well as to the use ofcertain ethers in fuel compositions for new purposes.

BACKGROUND TO THE INVENTION

Many diesel fuel compositions contain cetane boost components, alsoknown as ignition improvers. The cetane number of a fuel or fuelcomposition/formulation is a measure of its ease of ignition. With alower cetane number fuel a compression ignition (diesel) engine tends tobe more difficult to start and may run more noisily when cold. There isa general preference therefore for a diesel fuel composition to have ahigh cetane number, and as such automotive diesel specificationsgenerally stipulate a minimum cetane number.

It is also desirable, in the interest of the environment, to increasethe amount of biofuels or biocomponents used in automotive diesel fuels.Biofuels are combustible fuels, derived from biological sources, whichresult in a reduction in “well-to-wheels” (ie from source to combustion)greenhouse gas emissions. For use in diesel engines, fatty acid alkylesters (FAMEs), in particular fatty acid methyl esters (FAMEs) such asrapeseed methyl ester, soybean methyl ester and palm oil methyl ester,are the biofuels most commonly blended with conventional diesel fuelcomponents.

It is known in the art that certain (FAAEs), in particular FAMEs, can beused in low concentrations as cetane boost components in diesel fuels.

Currently FAMEs concentrations in light duty automotive diesel arelimited to a maximum of 7% v/v, primarily because of transfer of theester into the vehicle's sump, where its accumulation causes a dilutionof, and property changes in, the lubricating oil. This is a consequenceof both the high boiling points of FAMEs (typically of the order of 340°C.) and possibly also their polarity. Moreover, due to the incompleteesterification of oils (triglycerides) during their manufacture, FAMEscan contain trace amounts of glycerides which on cooling can crystalliseout before the FAMEs themselves, causing fuel filter blockages andcompromising the cold weather operability of fuel compositionscontaining them.

In any event, from the perspective of improving cetane number, it isknown that the cetane boosting effect of FAMEs diminishes as the blendratio of FAME to base fuel is increased. The potential of FAMEs ascetane boost components is thus limited for more than one reason,necessitating additional cetane boost additives, at least in someapplications.

It would therefore be desirable to identify alternative cetane boostcomponents for use in diesel fuel compositions, which suffer from fewerof the drawbacks and limitations associated with FAAEs.

It is an object of the invention to address one or more of thelimitations associated with prior art cetane boost components.

SUMMARY OF THE INVENTION

It has now been found that certain types of ethers can be particularlyadvantageous for use in diesel fuel compositions, particularly at highconcentrations, due to their effects on cetane numbers in fuel blends.

According in one embodiment of the invention, a fuel composition isprovided comprising: a diesel base fuel; from 1 to 10% v/v of a fattyacid alkyl ester; and more than 10% v/v of an ether component, saidether component comprising one or more ether compounds having in therange of from 8 to 12 carbon atoms and selected from compounds offormula I

R₁—O—R₂  (I)

wherein R₁ and R₂ are independently primary or secondary alkyl.

In another embodiment is provided, a method of increasing theconcentration of a biofuel component in a diesel fuel compositioncomprising blending more than 10% v/v of an ether compounds having inthe range of from 8 to 12 carbon atoms and selected from compounds offormula I

R₁—O—R₂  (I)

wherein R₁ and R₂ are independently primary or secondary alkyl.

DETAILED DESCRIPTION OF THE INVENTION

Ideally such components should be biologically derivable, ie biofuels,and also have minimal transfer into the engine sump and cause minimaldilution of lubricant as a result.

Cetane boost components need to offer a good property fit withfossil-derived diesel fuels, not only in terms of their cetane numberbut also in terms of volatility, flash point, melting and boiling pointsand cold flow properties. Flash point in particular can be a handlingissue for diesel fuels, and in an overall fuel composition must be abovea specified limit to ensure that flammable mixtures of fuel and air donot form within the fuel supply and distribution system. The meltingpoint of a molecule, meanwhile, will directly affect the cloud point andcold filter plugging point of a fuel composition into which it isblended, and these properties must also be controlled in order to allowsatisfactory vehicle operability during winter months.

Ideally, an alternative cetane boost component, particularly if it is abiofuel oxygenate component, will have properties—in particular a flashpoint and melting point—which allow it to be blended into diesel fuelcompositions at concentrations above the current 7% v/v limit for FAMEs.

U.S. Pat. No. 5,520,710 in the name of Olah suggests symmetrical orunsymmetrical ethers comprising 2 to 24 carbon atoms as cetane enhancingsupplements. The ether supplements are added in an amount of 0.5-10 v/v%, preferably 1-5% v/v. Data provided in U.S. Pat. No. 5,520,710 inrelation to dihexyl ether and dioctyl ether suggests that theeffectiveness of ethers as cetane boost additives reduces considerablywith increasing concentration, e.g. at a concentration of 5% v/vcompared to at a concentration of 2% v/v. This work contrasts with thatof U.S. Pat. No. 2,221,839 which considers the use of straight-chainaliphatic ethers as fuels or as ignition accelerators for compressionignition engine fuels. One example documents the ignition accelerationactivity resulting from incorporating one of 10% v/v n-butyl ether, 25%v/v n-amyl ether, and 25% v/v mono-butyl ether of diethylene glycol.Increase in cetane number is used as an indicator for usefulness as anignition accelerator.

In US 2002/0134008, it is proposed to provide a diesel fuel formulationsof a pre-determined flash point and cetane number increase by includingtwo oxygenate compounds, a first oxygenate of lower flash point than thediesel base fuel and of equal to or higher cetane number, and a secondoxygenate having a higher than or equal flash point to that of thediesel base fuel and a higher cetane number. The first oxygenatesproposed are selected from monoglyme, diethylether and diisopropyletherand are utilised in bulk quantities; the second oxygenate proposed isselected from diglyme, triglyme and dipentylether and is proposed foruse in quantities of 10% v/v or less.

Anastopoulos et al in Fuel 81 (2002) 1017-1024 ‘The tribiologicalbehaviour of alkyl ethers and alcohols in low sulphur automotive diesel’reviews the behaviours of seven alkyl ethers and five alcohols on thelubricity of automotive diesel. Their results led them to the conclusionthat alcohols offer the best lubricant potential, as only six of theseven ethers tested provided a benefit and then at concentrations of theorder of 750 to 1500 ppm.

According in one embodiment of the present invention there is provided afuel composition comprising: a diesel base fuel; from 1 to 10% v/v of afatty acid alkyl ester; and more than 10% v/v of an ether component, theether component comprising or consisting of one or more ether compoundshaving in the range of from 8 to 12 carbon atoms and selected fromcompounds of formula I

R₁—O—R₂  (I)

wherein R₁ and R₂ are independently C₂ to C₁₀ primary or secondaryalkyl. By ether compounds are meant compounds that contain only oneether group. The term “consisting” wherever used herein also embraces“consisting substantially”, but may optionally be limited to its strictmeaning of “consisting entirely”.

Contrary to the trend visible in U.S. Pat. No. 5,520,710, it has beenfound that C8+ ethers can function highly effectively as cetane boostadditives in diesel fuel at high concentrations in excess of 10% v/ve.g. up to 50% v/v. The ether component may be a biofuel and generallydoes not suffer from the drawbacks associated with FAAEs in the contextof lubricant dilution. For example, the ether component is less prone toaccumulation in vehicle sumps. The ether component can thus beincorporated into diesel fuel compositions at concentrationssignificantly higher than the current 7% v/v FAME limit, withoutbuild-up of biofuel components in engine oil and whilst maintaining apositive effect on cetane numbers of the overall compositions.

The ether component is to be understood herein as an added component.Preferably, the ether component may be, or be taken to be, the solesource of the ether compound(s) that it consists of in the composition,but this is not essential.

The ether component is defined herein as comprising or consisting of oneor more ether compounds having at least 8 carbon atoms (C8+ ether), orat least 9 carbon atoms (C9+ ether), or most preferably at least 10carbon atoms (C10+ ether). Thus, in preferred embodiments of theinvention, the ether component may comprise, or be, C8+ ether, C9+ether, or C10+ ether. Higher molecular weight ethers tend to haveparticularly advantageous volatility and cetane properties.

In some embodiments of the invention, the ether compounds of the ethercomponent may comprise at most 12 carbon atoms, or most preferably atmost 10 carbon atoms. Ether compounds with a relatively low number ofcarbon atoms may be preferred for their ease of biological synthesis.C10 ethers, are particularly preferred.

The ether compound(s) of the ether component may be symmetrical orasymmetrical; dialkyl, dicycloalkyl, or alkylcycloalkyl. Symmetricalcompounds are preferred. A particularly preferred ether is dipentylether (DPE).

Suitably, the ether compound(s) may be selected from compounds offormula I

R₁—O—R₂  (I)

wherein R₁ and R₂ are independently C₂ to C₂₄ primary or secondaryalkyl, provided that the total number of carbon atoms in formula (I) isas required, e.g. at least 8, 9 or 10, or as defined anywherehereinabove.

Preferably, R₁ and/or R₂ may be C₃ to C₁₅ alkyl, more preferably C₄ toC₇. In a particularly preferred embodiment, R₁ and/or R₂ may be C₅alkyl.

Since the ether component may preferably comprise or consist ofsymmetrical compounds, R₁ and R₂ may preferably be the same.

The ether component may comprise or consist of one or more of the ethercompounds or ether compound mixtures described hereinabove. Mostpreferably, the ether component may comprise or consist of dipentylether.

The ether component may comprise a mixture of two or more ethercompounds as defined hereinabove. For predictability of properties, insome embodiments of the invention, the ether component may comprise atleast 50% v/v, or 70% v/v or 90% v/v, or even 95% v/v of any one of theether compounds or ether compound mixtures described hereinabove.

In some embodiments of the invention, the ether component may beaccompanied by a small amount of impurities, for example by-products ofether synthesis that have no substantive effect on the overallproperties of the ether component. Such impurities may, for example, bepresent in an amount of at most about 3%, e.g. as measured by gaschromatography (GC) commonly employed by suppliers such as SigmaAldrich. In embodiments of the invention, such impurities up to 3% asmeasured by GC may be considered part of the ether component, in whichcase the component consists substantially of the ether compounds.

The cetane number of the ether component will typically be higher thanthe cetane number of the diesel base fuel. Suitably, the cetane numberof the ether component may be at least 90, preferably at least 100, orat least 102, most preferably at least 104.

Suitably, the ether component may offer a good property fit with thediesel base fuel, particularly with a view to the composition meetingEN590 or another specification.

The ether component may preferably have a density, measured according toASTM D 4052, of at least 0.750 g/cm³, more preferably at least 0.770g/cm³. The density of the ether component may, for example, be at most0.830 g/cm³.

The ether component may preferably have a flash point, measuredaccording to ASTM D 93, of at least 20° C., more preferably at least 50°C.

The ether component may preferably have a vapour pressure, measured at25° C., of at most 500 Torr (66661.2 Pa), preferably at most 50 Torr(6666.1 Pa), or even at most 5 Torr (666.6 Pa). The vapour pressure ofthe ether component may, for example, be at least 0.5 Torr (66.6 Pa).

The ether component may preferably have a boiling point, measuredaccording to ASTM D 86, of at least 40° C., more preferably at least100° C. The boiling point of the ether component may, for example, be atmost 480° C.

The ether component may be prepared by any suitable process known in theart. One well known synthesis is the Williamson ether synthesis, whichinvolves treatment of a parent alcohol with a strong base to form analkoxide, followed by addition of an appropriate aliphatic compoundbearing a leaving group such as halide or sulfonate. This synthesisworks particularly well for acyclic, unencumbered open chain primaryaliphatic compounds. The Ullmann ether synthesis, which is also wellknown and based on a similar mechanism, albeit generally in the presenceof a catalyst, is particularly suitable for the formation of arylethers. Other methods of forming ethers include the electrophilicaddition of alcohols to alkenes, e.g. alkoxymercuration of alkenes usingmercury trifluoroacetate as catalyst and hydroboration of alkenesfollowed by oxidation. Further methods of synthesizing ethers, includingcyclic and polycyclic systems are described, for example, in U.S. Pat.No. 5,520,710.

On an industrial scale, symmetrical ethers are typically prepared by thedehydration of a parent alcohol. Dipentyl ether, for example, may beprepared by dehydrating 1-pentanol in the presence of sulphuric acid.

The alcohols or other starting materials for the synthesis of ethers maybe obtained from any available source. For example parent alcohols, suchas amyl alcohol, may be obtained by the hydroformylation of olefins,which may in turn be petroleum derived (see e.g. K Weissermel and H-JArpe, Industrial Organic Chemistry, Wiley-Vch, p 205). Furtheralternatives may be i) Markovnikov hydration of olefins in the presenceof acids and/or metal catalysts; ii) Anti-Markovnikov addition via thesequence hydroboration/oxidation of alkenes (see e.g. M. G. Loudon,(2002). “Addition Reactions of Alkenes”. Organic Chemistry (FourthEdition ed.) Oxford University Press pp. 168); iii) the reduction oforganic acids (such as but not limited to acids obtained viafermentation), via intermediates aldehydes (see e.g. Y. Li, et al.Huaxue Tongbao (2002), 65(7), 452-457); and iv) deep hydrogenation offurfural through intermediates such as methylfuran and methyltetrahydrofuran (see e.g. H.-Y. Zheng, et al, Journal of MolecularCatalysis A: Chemical, 246(1-2), 18-23; 2006).

In a preferred embodiment of the invention, the ether component may be abiofuel component, ie derived from a biological source. In suchembodiments, the ether component may comprise or consist of ethercompounds derived from parent molecules, e.g. alcohols, which are inturn obtained from a renewable carbonaceous feedstock. For example, itis known to obtain alcohols by fermentation, e.g. by distillation offusel oil. Other biological routes to alcohols, such as pentanol, viafermentation of renewable feedstocks (organic carbon sources) usingmicroorganisms, fungi (such as members of the genus Saccharomyces),protists, algae, bacteria (including cyanobacteria) and archaea areincreasingly being proposed. Alternatively, alcohols can be biologicallyderived via gasification/pyrolysis from renewable carbonaceousfeedstock, followed by Fischer-Tropsch synthesis.

In some embodiments of the invention, the ether component may compriseat least about 0.1 dpm/gC of carbon-14. It is known in the art thatcarbon-14, which has a half-life of about 5700 years, is found inbiologically derived materials but not in fossil fuels. Carbon-14 levelscan be determined by measuring its decay process (disintegrations perminute per gram carbon or dpm/gC) through liquid scintillation counting.

The concentration of the ether component in the overall fuel composition(or at least in the base fuel/ether component mixture) is preferably 90%v/v or less, more preferably 80% v/v or less, yet more preferably 70 or60 or 50% v/v or less, based on the total composition/mixture. As aminimum it is more than 10% v/v, or 12% v/v or greater, such as 15% or25% v/v or greater, or even 30 or 40% v/v or greater, based on the totalcomposition/mixture. The amount of the ether component may represent abalance of the fuel composition: after inclusion of the base fuelcomponent, and any further (optional) components and additives, theether component may therefore be present in an amount to represent thebalance to 100% v/v in the composition.

The diesel base fuel may be any fuel component, or mixture thereof,which is suitable and/or adapted for use in a diesel fuel compositionand therefore for combustion within a compression ignition (diesel)engine. It will typically be a liquid hydrocarbon middle distillatefuel, more typically a gas oil. It may be or contain a kerosene fuelcomponent.

It may be petroleum derived. Alternatively it may be synthetic: forinstance it may be the product of a Fischer-Tropsch condensation. It maybe derived from a biological source.

A diesel base fuel will typically boil in the range from 150 or 180 to370° C. (ASTM D86 or EN ISO 3405). It will suitably have a measuredcetane number (ASTM D613) of from 40 to 70 or from 40 to 65 or from 51to 65 or to 70.

However, because the ether component has a positive effect on cetanenumber, a fuel composition according to the invention may include (ormay include a greater proportion of) a base fuel which has a relativelylow cetane number. This can increase the options available to the fuelformulator. The ether component may therefore be used for the purpose ofallowing the inclusion, in a diesel fuel composition, of one or morelower cetane number fuel components (for example diesel base fuels), orof a higher concentration of one or more such fuel components, without,or without undue, detriment to the cetane number of the overallcomposition. In this context a “lower cetane number” fuel component mayfor example have a measured cetane number of less than 50, or of lessthan 45 or 40 or in cases of less than 35. “Without undue detriment tothe cetane number” may for example mean without reducing the cetanenumber by more than 30%, or in cases by more than 20 or 10 or 5 or 1%,of its value if a higher cetane number fuel component (for example, witha measured cetane number of 40 or greater, or of 45 or 50 or greater)were to be used in the fuel composition, at the same concentration, inplace of the lower cetane number fuel component. It may entail theoverall fuel composition meeting a desired target specification, forexample the European diesel fuel specification EN 590.

The diesel base fuel may suitably be present in the composition in anamount of 10% v/v or greater, or 20 or 30 or 40% or 50% v/v or greater,based on the total composition. It may be present in an amount of lessthan 90% v/v, or up to 85 or up to 80 or 75% v/v, or up to 70 or 65 or60% v/v, based on the total composition. The amount of the base fuel mayrepresent a balance of the fuel composition: after inclusion of theether component, the fatty acid alkyl ester, and any further (optional)components and additives, the diesel base fuel may therefore representthe balance to 100% v/v in the composition.

The fuel composition may be prepared by simple blending of itscomponents in any suitable order, and such methods of blending any ofthe fuel compositions herein are embraced by the invention.

The fuel composition may comprise, in addition to the diesel base fuel,the fatty acid alkyl ester, and the ether component, one or more fuel orrefinery additives, in particular additives which are suitable for usein automotive diesel fuels. Many such additives are known andcommercially available. The composition may for example comprise one ormore additives selected from cetane boost additives, antistaticadditives, lubricity additives, cold flow additives, and combinationsthereof. Such additives may be included at a concentration of up to 300ppmw (parts per million by weight), for example of from 50 to 300 ppmw.Due to the inclusion of the ether component, however, it may, asdescribed below, be possible for the composition to contain lower levelsof cetane boost additive, or in cases for the composition not to containsuch type of additive.

The fuel composition should be suitable and/or adapted for use in acompression ignition (diesel) internal combustion engine. It may inparticular be an automotive fuel composition. In further embodiments itmay be suitable and/or adapted for use as an industrial gas oil, or as adomestic heating oil.

The fuel composition may suitably comply with applicable currentstandard diesel fuel specification(s) such as for example EN 590 (forEurope) or ASTM D975 (for the USA). By way of example, the overallcomposition may have a density from 820 to 845 kg/m³ at 15° C. (ASTMD4052 or EN ISO 3675); a T95 boiling point (ASTM D86 or EN ISO 3405) of360° C. or less; a measured cetane number (ASTM D613) of 40 or greater,ideally of 51 or greater; a kinematic viscosity at 40° C. (VK40) (ASTMD445 or EN ISO 3104) from 2 to 4.5 centistokes (mm²/s); a flash point(ASTM D93 or EN ISO 2719) of 55° C. or greater; a sulphur content (ASTMD2622 or EN ISO 20846) of 50 mg/kg or less; a cloud point (ASTM D2500/IP219/ISO 3015) of less than −10° C.; and/or a polycyclic aromatichydrocarbons (PAH) content (EN 12916) of less than 11% w/w. It may havea lubricity, measured using a high frequency reciprocating rig forexample according to ISO 12156 and expressed as a “HFRR wear scar”, of460 μm or less.

Relevant specifications may however differ from country to country andfrom year to year, and may depend on the intended use of thecomposition. Moreover the composition may contain individual fuelcomponents with properties outside of these ranges, since the propertiesof an overall blend may differ, often significantly, from those of itsindividual constituents.

The fuel composition comprises, in addition to the diesel base fuel andthe ether component, a fatty acid alkyl ester, in particular a fattyacid methyl ester (FAME) such as rapeseed methyl ester or palm oilmethyl ester. It is further possible for one or more further biofuelcomponents, particularly other than ether or FAME, to be present. Thebiofuel component may suitably comprise an alcohol, for example ethanol,and/or a fatty alcohol ester, and/or a hydrogenated vegetable oil. Thefatty acid alkyl ester may be present in an amount of at least 1% v/v,or 2 or 3 or 4 or 5% v/v, and up to 10 or 7 or 5% v/v, based on thetotal composition. Typically, the amount of further biofuel componentmay be at least 1% v/v, or 2 or 3 or 4 or 5% v/v, and up to 30% v/v, orup to 20 or 10 or 7 or 5% v/v, based on the total composition. Due tothe inclusion of the ether component, it may, as described below, bepossible for the composition to contain lower levels of biofuelcomponents, or in cases for the composition not to contain additionalbiofuel components.

It has been found that the ether component can significantly boostcetane number when the fuel composition also comprises a a fatty acidalkyl ester.

According to a further aspect of the invention, there is provided theuse of an ether component as defined above, in a diesel fuel compositioncontaining a fatty acid alkyl ester, for the purpose of increasing thecetane number of the composition.

If it is desired to include a fatty acid ester or a fatty alcohol esterin a diesel fuel composition, for example in order to increase thebiofuel content of the composition, and/or for the lubricity benefitsdescribed in US-A-2011/0154728, the present invention can provide for afurther cetane boost. In accordance with the invention, the ethercomponent may be used to replace all or part of a fatty acid ester orfatty alcohol ester which was previously, or was intended to be, orwould otherwise have been, included in the diesel fuel composition.

The ether component may be used to achieve any degree of increase in thecetane number of the diesel fuel composition, and/or for the purpose ofachieving a desired target cetane number, for example a target set by anapplicable regulatory standard such as EN 590, or a target set by a user(which includes a handler, keeper or distributor) or potential user ofthe composition. It may be used to achieve a cetane number increasewhich is greater than that which would be possible using the sameconcentration of another biofuel component, in particular of a fattyalcohol ester such as an alkyl acetate, or of a fatty acid alkyl estersuch as a FAME. The increase in cetane number will typically be ascompared to the cetane number of the composition prior to adding ethercomponent to it.

In the present context, “achieving” a desired target property alsoembraces—and in an embodiment involves—improving on the relevant target.Thus, for example, the ether component may be used to produce a dieselfuel composition which has a cetane number higher than a desired targetstandard.

The cetane number of a fuel composition may be determined using anysuitable method, for instance using the standard test procedure ASTMD613 (ISO 5165, IP 41) which provides a so-called “measured” cetanenumber obtained under engine running conditions. Alternatively thecetane number may be determined using the more recent “ignition qualitytest” (IQT) (ASTM D6890, IP 498), which provides a “derived” cetanenumber based on the time delay between injection and combustion of afuel sample introduced into a constant volume combustion chamber. Thisrelatively rapid technique can be used on laboratory scale (ca 100 ml)samples of a range of different fuels.

Alternatively, cetane number may be measured by near infraredspectroscopy (NIR), as for example described in U.S. Pat. No. 5,349,188.This method may be preferred in a refinery environment as it can be lesscumbersome than for instance ASTM D613. NIR measurements make use of acorrelation between the measured spectrum and the actual cetane numberof a sample. An underlying model is prepared by correlating the knowncetane numbers of a variety of fuel samples with their near infraredspectral data.

The present invention preferably results in a diesel fuel compositionwhich has a measured cetane number (ASTM D613) of 40 or greater, or of45 or 50 or 51 or greater, for example of 55 or 60 or 65 or greater, incases of 70 or 75 or greater.

The invention may additionally or alternatively be used to adjust anyproperty of the diesel fuel composition which is equivalent to orassociated with cetane number, for example to improve the combustionperformance of the composition (eg to shorten ignition delays, tofacilitate cold starting and/or to reduce incomplete combustion and/orassociated emissions in a fuel-consuming system running on the fuelcomposition) and/or to improve fuel economy.

By using the present invention, it can be possible to include in adiesel fuel composition a higher concentration of a biofuel componentthan would have been predicted to be possible—whilst still achieving adesired target cetane number—based on the properties of the fattyacid/alcohol esters. It can be desirable to increase biofuelconcentrations for a number of reasons, for instance to meet regulatoryrequirements or consumer expectations or more generally to reduce the“well-to-wheels” carbon dioxide emissions associated with the productionand use of the fuel. It can also be desirable to increase theconcentration of fatty alcohol esters, not only as biofuel componentsbut also, for example, in order to improve the lubricity of a fuelcomposition containing an acid-based lubricity additive, as described inUS-A-2011/0154728. However it would have been thought necessary, in thepast, to balance such benefits against the potential reduction in cetanenumber which would be expected to result from increasing theconcentration of a fatty alcohol ester, particularly for those estershaving shorter (for example C10 or less) carbon chains. According to thepresent invention, such benefits can now be achieved with the addedoption of a cetane number increase and without leading to excessivelubricant dilution.

Thus according to an additional aspect, the invention provides the useof an ether component as defined above, in a diesel fuel composition,for the purpose of increasing the concentration of a biofuel componentin the composition, without undue detriment to: the cetane number of thecomposition; and/or lubricant dilution under engine operatingconditions. The biofuel component may, for example, comprise a fattyalcohol ester: the ether component may therefore be used to increase theconcentration of fatty alcohol esters in the diesel fuel composition,without or without undue detriment to its cetane number and/or lubricantdilution properties under engine operating conditions. Alternatively,the biofuel component may be taken as including all biologically derivedfuel components in the composition. In this way the invention may beused to increase the options available, to the fuel formulator, forincreasing the biofuel content of a diesel fuel composition whilst stillmeeting relevant fuel specifications.

In the present context, “without undue detriment to the cetane number”may for example mean without reducing the cetane number by more than30%, or in cases by more than 20 or 10 or 5 or 1%, of its originalvalue.

In the present context, “without undue detriment to lubricant dilutionunder engine operating conditions” may for example mean withoutincreasing at all the lubricant dilution compared to a comparable oridentical fuel composition without the ether component. Lubricantdilution may be measured in any suitable manner, e.g. based on gaschromatography (GC) analysis of lubricant sump samples. Expressed inanother way, the ether component may be used to enhance or maintainlubricant lifetime during use of the composition, or to maintain orincrease the oil drain interval.

In accordance with this embodiment of the invention, the ether componentmay be used to achieve any degree of increase in the concentration ofthe relevant biofuel component. In an embodiment, the ether component isused to increase the concentration of the biofuel component whilst atthe same time increasing (which again embraces any degree of increase)the cetane number of the diesel fuel composition.

Because the ether component can increase the cetane number of a dieselfuel composition in which it is used, the composition may as aconsequence require a lower level of cetane boost additives than mightotherwise have been needed in order to achieve a desired target cetanenumber. This can in turn reduce the cost and complexity of preparing thecomposition, and/or can provide greater versatility in fuel formulationpractices. Thus, a further aspect of the invention provides the use ofan ether component as defined above in a diesel fuel composition, forthe purpose of reducing the concentration of a cetane boost additive inthe composition.

In the context of this embodiment of the invention, the term “reducing”embraces any degree of reduction, including reduction to zero. Thereduction may for instance be 10% or more of the original concentrationof the cetane boost additive, or 25 or 50 or 75 or 90% or more. Thereduction may be as compared to the concentration of the cetane boostadditive which would otherwise have been incorporated into the fuelcomposition in order to achieve the properties and performance requiredand/or desired of it in the context of its intended use. This may forinstance be the concentration of the additive which was present in thecomposition prior to the realisation that the ether component could beused in the way provided by the present invention, and/or which waspresent in an otherwise analogous fuel composition intended (egmarketed) for use in an analogous context, prior to adding the ethercomponent to it in accordance with the invention.

The reduction in concentration of the cetane boost additive may be ascompared to the concentration of the additive which would be predictedto be necessary to achieve a desired cetane number for the compositionin the absence of the ether component.

A cetane boost additive may be any additive which is capable ofincreasing, or intended to increase, the cetane number of a diesel fuelcomposition to which it is added, and/or to improve the ignitionproperties of such a composition when it is used in an engine or otherfuel-consuming system. A cetane boost additive may also be known as acetane improver, a cetane number improver or an ignition improver. Manysuch additives are known and commercially available; they typicallyfunction by increasing the concentration of free radicals when a fuelbegins to react in a combustion chamber of a fuel-consuming system.Examples include organic nitrates and nitrites, in particular(cyclo)alkyl nitrates such as isopropyl nitrate, 2-ethylhexyl nitrate(2-EHN) and cyclohexyl nitrate, and ethyl nitrates such as methoxyethylnitrate; and organic (hydro)peroxides such as di-tert-butyl peroxide.Cetane boosting diesel fuel additives are commercially available forinstance as HITEC™ 4103 (ex Afton Chemical) and as CI-0801 and CI-0806(ex Innospec Inc).

In the context of the present invention, “use” of the ether component ina diesel fuel composition means incorporating the ether component intothe composition, typically as a blend (ie a physical mixture) with oneor more other diesel fuel components, for example a diesel base fuel andoptionally one or more diesel fuel additives. The ether component willconveniently be incorporated before the composition is introduced intoan engine or other system which is to be run on the composition. Insteador in addition, the use of the ether component may involve running afuel-consuming system, typically an internal combustion engine, on adiesel fuel composition containing the ether component, typically byintroducing the composition into a combustion chamber of an engine. Itmay involve running a vehicle which is driven by a fuel-consumingsystem, on a diesel fuel composition containing the ether component. Insuch cases the engine is suitably a compression ignition (diesel)engine.

“Use” of the ether component in the ways described above may alsoembrace supplying the ether component together with instructions for itsuse in a diesel fuel composition in order to increase the cetane numberof the composition. The ether component may itself be supplied as partof a composition which is suitable for and/or intended for use as a fueladditive, in which case the ether component may be included in such acomposition for the purpose of influencing its effects on the cetanenumber of a diesel fuel composition.

In general, references to “adding” a component to, or “incorporating” acomponent in, a fuel composition may be taken to embrace addition orincorporation at any point during the production of the composition orat any time prior to its use.

In embodiments, the present invention may be used to produce at least1,000 litres of the ether component-containing fuel composition, or atleast 5,000 or 10,000 or 20,000 or 50,000 litres.

A fuel composition prepared or used according to the invention may bemarketed with an indication that it benefits from an improvement due tothe inclusion of the ether component, in particular a higher cetanenumber. The marketing of such a composition may comprise an activityselected from (a) providing the composition in a container thatcomprises the relevant indication; (b) supplying the composition withproduct literature that comprises the indication; (c) providing theindication in a publication or sign (for example at the point of sale)that describes the composition; and (d) providing the indication in acommercial which is aired for instance on the radio, television orinternet. The improvement may be attributed, in such an indication, atleast partly to the presence of the ether component. The invention mayinvolve assessing the relevant property (in particular the cetanenumber) of the composition during or after its preparation. It mayinvolve assessing the relevant property both before and afterincorporation of the ether component, for example so as to confirm thatthe ether component contributes to the relevant improvement in thecomposition.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, mean “including but not limited to”, anddo not exclude other moieties, additives, components, integers or steps.Moreover the singular encompasses the plural unless the contextotherwise requires: in particular, where the indefinite article is used,the specification is to be understood as contemplating plurality as wellas singularity, unless the context requires otherwise.

Preferred features of each aspect of the invention may be as describedin connection with any of the other aspects. Other features of theinvention will become apparent from the following examples. Generallyspeaking the invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims and drawings). Thus features, integers,characteristics, compounds, chemical moieties or groups described inconjunction with a particular aspect, embodiment or example of theinvention are to be understood to be applicable to any other aspect,embodiment or example described herein unless incompatible therewith.For example, for the avoidance of doubt, the optional and preferredfeatures of the fuel composition, the diesel base fuel, the ethercomponent or the biofuel component apply to all aspects of the inventionin which the fuel composition, the diesel base fuel, the ether componentor the biofuel component are mentioned.

Moreover unless stated otherwise, any feature disclosed herein may bereplaced by an alternative feature serving the same or a similarpurpose.

Where upper and lower limits are quoted for a property, for example forthe concentration of a fuel component, then a range of values defined bya combination of any of the upper limits with any of the lower limitsmay also be implied.

In this specification, references to fuel and fuel component propertiesare—unless stated otherwise—to properties measured under ambientconditions, ie at atmospheric pressure and at a temperature from 16 to22 or 25° C., or from 18 to 22 or 25° C., for example about 20° C.

The present invention will now be further described with reference tothe following non-limiting examples.

Example 1 (Comparative)

Diesel fuel compositions were prepared by blending a diesel base fuelwith an ether component consisting of dipentyl ether (DPE).

The base fuel was a zero sulphur diesel fuel (ex Shell), which conformedto the European diesel fuel specification EN 590. It did not contain anydetergent or lubricity additives, or any oxygenates such as FAMEs. Itsproperties are summarised in Table 1 below.

TABLE 1 Property Units Test method Base fuel Density @ 15° C. kg/m³ ASTMD 4052 825 VK40 mm²/s IP 71 2.08 Distillation ASTM D 86  0% ° C. 172.0 10% 195.6  20% 205.3  30% 215.0  40% 226.7  50% 239.9  60% 254.4  70%269.6  80% 288.2  90% 311.2  95% 328.6 100% 342 Rec at 250° C. % v/v57.5 Rec at 370° C. % v/v 97.7 Cetane (CRF engine) ASTM 613 53.8 Derivedcetane (IQT) IP 498 54.1 HFRR (averaged) μm ISO 12156 272

The ether component tested consisted of 97% pure (measured by GC)dipentyl ether sourced from Sigma Aldrich. Relevant properties(literature values) for the ether component are as follows: boilingpoint=188° C.; flash point=57° C.; vapour pressure at 25° C.=1.0 Torr;density=0.791 g/cm³.

The ether component was blended with the base fuel at 2, 5, 10, 15, 30and 50% v/v. The resultant blends were tested for cetane number usingthe IQT method specified in Table 1. The results are shown in Table 2.

From the measured cetane numbers of the blends and the diesel base fuel,blending cetane number values were calculated for the ether component asfollows.

blending CN _(DPE)=(CN _(comp)−(1−x)*CN _(diesel))/x

where:

-   -   blending CN_(DPE) is the blending cetane number of the ether        component when used at volume fraction x;    -   CN_(comp) is the measured cetane number of the base fuel/ether        component blend; and    -   CN_(diesel) is the measured cetane number of the diesel base        fuel.

The resultant blend values are also shown in Table 2.

TABLE 2 Diesel DPE CN_(comp) Blending Comp (% v/v) (% v/v) (IQT)CN_(DPE) 1 98 2 55.3 99.4 2 95 5 56.6 98.4 3 90 10 58.1 91.4 4 85 1560.4 94.4 5 70 30 66.6 95.1 6 50 50 76.7 99.0

The blending cetane number of the ether component is a measure of thecontribution of the ether component to the measured cetane number of thefuel composition. It can be seen that the blending cetane number of theether component increases from 91.4 at 10% v/v to 99 at 50% v/v. Theeffectiveness of the ether component in boosting cetane is thusincreased at higher concentrations.

Example 2 (Comparative)

Diesel fuel compositions were prepared, for comparison with those ofExample 1, by blending a diesel base fuel with a fatty acid methyl ester(FAME) component.

The diesel base fuel was as in Example 1.

The FAME component consisted of 100% refinery grade palm oil methylesters (POME).

Relevant properties for the FAME component are as follows: flashpoint=156° C. (IP 34); viscosity at 40° C.=4.45 mm²/s (IP 71);density=0.877 g/cm³ (IP 365).

The FAME component was blended with the base fuel at 2, 5, 10, 15, 30and 50% v/v. The resultant blends were tested for cetane number usingthe IQT method specified in Table 1. The results are shown in Table 3.

From the measured cetane numbers of the blends and the diesel base fuel,blending cetane number values were calculated for the FAME component asfollows.

blending CN _(FAME)=(CN _(comp)−(1−x)*CN _(diesel))/x

where:

-   -   blending CN_(FAME) is the blending cetane number of the FAME        component when used at volume fraction x;    -   CN_(comp) is the measured cetane number of the base fuel/ether        component blend; and    -   CN_(diesel) is the measured cetane number of the diesel base        fuel.

The resultant blend values are also shown in Table 3.

TABLE 3 Diesel FAME CN_(comp) Blending Comp (% v/v) (% v/v) (IQT)CN_(FAME) 7 98 2 54.7 69.4 8 95 5 56 86.4 9 90 10 56.5 75.4 10 85 1557.2 73.1 11 70 30 59.1 70.1 12 50 50 62.4 70.4

The blending cetane number of the FAME component is a measure of thecontribution of the FAME component to the measured cetane number of thefuel composition. It can be seen that the blending cetane number of theFAME component decreases from 75.4 at 10% v/v to 70.4 at 50% v/v. Theeffectiveness of the FAME component in boosting cetane is thus decreasedat higher concentrations.

Example 3

Diesel fuel compositions were prepared, according to the invention, byblending a diesel base fuel with an ether component consisting ofdipentyl ether and a fatty acid methyl ester (FAME) component.

The diesel base fuel and the dipentyl ether components were as inExample 1. The FAME component was as in Example 2.

The ether and FAME components were blended with the base fuel in theamounts shown in Table 4. The resultant blends were tested for cetanenumber using the IQT method specified in Table 1. The results are shownin Table 4.

From the measured cetane numbers of the blends and the diesel base fuel,blending cetane number values were calculated for the combined ether andFAME components as follows.

blending CN _(DPE+FAME)=(CN _(comp)−(1−x)*CN _(diesel))/x

where:

-   -   blending CN_(DPE+FAME) is the blending cetane number of the        combined ether and FAME components when used at a total volume        fraction x;    -   CN_(comp) is the measured cetane number of the base fuel/ether        component blend; and    -   CN_(diesel) is the measured cetane number of the diesel base        fuel.

The resultant blend values are also shown in Table 4.

TABLE 4 Diesel FAME DPE CN_(comp) Blending Comp (% v/v) (% v/v) (% v/v)(IQT) CN_(DPE+FAME) 13 90 5 5 56 70.4 14 85 5 10 58.7 83.1 15 70 5 25 6486.4 16 50 5 45 74.5 94.6 17 85 7.5 7.5 58.6 82.4 18 70 15 15 62.9 82.719 50 25 25 68.4 82.4

The blending cetane number of the combined ether and FAME components isa measure of the contribution of these components to the measured cetanenumber of the fuel composition. It can be seen that, at a consistentconcentration of the FAME component, the blending cetane number of thecombined components increases from 70.4 at 5% v/v ether component to94.6 at 45% v/v ether component. At equivalent concentrations of etherand FAME components, the blending cetane number of the combinedcomponents stays relatively constant, irrespective of concentration.

Example 4

The properties of a diesel fuel composition from Example 1 were examinedto determine their compliance with fuel specifications. Table 5 showsthe properties of composition 3 from Example 1.

TABLE 5 Property Units Test method Comp 3 Density @ 15° C. kg/m³ ASTM D4052 822 VK40 mm²/s IP 71 1.92 Distillation ASTM D 86  0% ° C. 174.3 10% 191.6  20% 198.8  30% 207.6  40% 218.1  50% 230.4  60% 246.7  70%264.7  80% 284.8  90% 309.3  95% 328.3 100% 340.3 Rec at 250° C. % v/v61.9 Rec at 370° C. % v/v 97 Flash point ° C. ASTM D 93 65 Cetane (CRFengine) ASTM D 613 56.8 Derived cetane (IQT) IP 498 58.4 HFRR (averaged)μm ISO 12156 445 Cloud point ° C. IP 219 −14 CFPP (pot A) IP 309 −35CFPP (pot B) IP 309 −35

Example 5

The dilution of diesel engine lubricant with ether component and otherbiofuel components was examined.

The standardised experimental procedure was as follows:

-   -   A diesel engine was flushed with new lubricant and operated for        16 hours under steady-state conditions. The engine speed and        load was then increased to a higher speed/load point at the        start of test, after which the lubricant sump temperature        reached 120° C.    -   The diesel fuel used to run the engine did not contain any        biofuels (ie. free of FAME and ether).    -   To simulate accumulation of a bio-component transferred from a        diesel fuel, known volumes of the ether component and/or FAME        component (as in the Examples above) were dosed in separate runs        directly into the lubricant sump.    -   Samples at the start, end and intermediate time points were        collected and analysed.

The components tested were Ether component only, FAME component only,and an equivolume Ether-FAME component mixture. The loss ofbio-component (measured as percentage remaining in the lubricant; %remaining) was determined from GC analysis of lubricant sump samples.

The results are shown in Table 6.

TABLE 6 Ether-FAME component Ether FAME (1:1 v/v) Time componentcomponent FAME % Ether % (min) % remaining % remaining remainingremaining 0 100 100 100 100 60 34.4 — — — 120 15.4 — — — 180 2.7 — — —240 2 — — — 300 0.1 — — — 360 0 — — — 420 0 94.3 95.5 0

It is observed that the ether component is volatilized from thelubricant in less than 7 hours, whereas the FAME component ispersistent. When an ether-FAME mixture is added, the ether component isvolatilized in the same manner as when it was present as a singlecomponent.

Discussion of Examples

The effectiveness of the ether component in boosting cetane has beenfound to increase at higher concentrations. This is unexpected, both inview of the behaviour of other cetane boost components such as FAME andin view of the behaviour of the ether component at concentrations below10% v/v. The ether component has been found to boost cetane effectivelyin diesel fuel compositions both with and without a FAME component, butprovided a significant boost when both components were present.

Furthermore, it was found that any dilution of lubricant by the ethercomponent was rapidly reversible by volatilization under engineoperating conditions. Therefore, lubricant performance properties suchas protection and durability are not affected. This behaviour of theether component contrasts with that of FAMEs, which accumulate in thelubricant.

We claim:
 1. A fuel composition comprising: a diesel base fuel; from 1to 10% v/v of a fatty acid alkyl ester; and more than 10% v/v of anether component, said ether component comprising one or more ethercompounds having in the range of from 8 to 12 carbon atoms and selectedfrom compounds of formula IR₁—O—R₂  (I) wherein R₁ and R₂ are independently primary or secondaryalkyl.
 2. The fuel composition of claim 1 wherein the ether componentcomprises symmetrical ether compounds.
 3. The fuel composition of claim1 wherein the ether component comprises dipentyl ether.
 4. The fuelcomposition of claim 1 wherein the ether component has a density of atleast 0.770 g/cm³.
 5. The fuel composition of claim 1 wherein the ethercomponent has a flash point of at least 50° C.
 6. The fuel compositionof claim 1 wherein the ether component has a vapour pressure at 25° C.of at most 5 Torr.
 7. The fuel composition of claim 1 wherein the ethercomponent has a boiling point of at least 100° C.
 8. The fuelcomposition of claim 1 wherein the ether component is a biofuelcomponent.
 9. The fuel composition of claim 1 wherein the ethercomponent is present in an amount of from 15% to 90% v/v.
 10. The fuelcomposition of claim 9 wherein the ether component is present in anamount of from 15% to 50% v/v.
 11. The fuel composition of claim 1wherein the ether component consists of one or more ether compoundshaving in the range of from 8 to 12 carbon atoms and selected fromcompounds of formula IR₁—O—R₂  (I) wherein R₁ and R₂ are independently primary or secondaryalkyl.
 12. The fuel composition of claim 1 wherein the ether componenthas a density of at least 0.770 g/cm³, a flash point of at least 50° C.,a vapour pressure at 25° C. of at most 5 Torr, and a boiling point of atleast 100° C.
 13. The fuel composition of claim 1 wherein the fuelcomposition has a measured cetane number of 40 or greater.
 14. A methodof increasing the concentration of a biofuel component in a diesel fuelcomposition comprising blending more than 10% v/v of an ether compoundshaving in the range of from 8 to 12 carbon atoms and selected fromcompounds of formula IR₁—O—R₂  (I) wherein R₁ and R₂ are independently primary or secondaryalkyl.
 15. The method of claim 14 wherein the diesel fuel compositioncontains a fatty acid ester or a fatty alcohol ester.